For materials processing by means of laser radiation, a laser processing device is employed in many cases for scanning the areas of the object which are to be processed with the laser beam. The precision in positioning the laser beam usually determines the precision achieved in processing. Exact three-dimensional positioning is required when focusing the laser beam into a processing volume. For high-precision processing, it is usually indispensable, therefore, to hold the object in an exactly defined position relative to the laser processing device.
For such applications, the above-mentioned adapter is useful, because it enables fixation of the object to be processed, so that defined ratios can be achieved up to the processing volume. The central region of the adapter thus becomes part of the beam path.
This is necessary, in particular, in micro-processing of materials which have only low linear optical absorption in the spectral range of the processing laser radiation. In such materials, usually non-linear interactions between the laser radiation and the material are utilized generally in the form of an optical breakthrough being generated in the focus of the laser beam. Since the processing effect then only occurs in the laser beam focus, exact three-dimensional positioning of the focal point is indispensable. Thus, exact depth adjustment of the focal position in the beam path is required in addition to two-dimensional deflection of the laser beam. The above-mentioned adapter serves to ensure constant optical conditions and ones that are known with a certain precision in the beam path leading to the object by the central region of the adapter being part of the beam path and the adapter coupling the object and the laser processing device.
A typical application for such an adapter is the ophthalmic surgery method known as femtosecond LASIK, wherein the laser processing device focuses a laser beam to a focal point on the order of a few micrometers into the cornea. A plasma causing local separation of corneal tissue is then generated in the focus. By suitable sequential arrangement of the zones of local separation thus generated, macroscopic cuts are realized and a determined partial volume of the cornea is isolated. Then, by removal of said partial volume, a desired change in refraction of the cornea is achieved, thus enabling correction of defective eyesight.
For this LASIK method, a contact lens provided with reference marks is known from U.S. Pat. No. 6,373,571. This contact lens is adjusted by means of a separate measurement device, thus leading to a relatively complex design. An example of an adapter of the aforementioned type is described in EP 1 159 986 A2. While being similar to the contact lens of U.S. Pat. No. 6,373,571, it additionally comprises a periphery as well in the form of a holder having hair marks, which allow visual alignment by the surgeon.